chore(lint): add std instead of core/alloc lints to ratatui-core (#1759)

Resolves #1752

ratatui-core/src/lib.rs

@@ -38,6 +38,10 @@
 //!
 //! This project is licensed under the MIT License. See the [LICENSE](../LICENSE) file for details.
 
+#![warn(clippy::std_instead_of_core)]
+#![warn(clippy::std_instead_of_alloc)]
+#![warn(clippy::alloc_instead_of_core)]
+
 extern crate alloc;
 
 pub mod backend;